Mixed species toxicity tests to monitor the impact of leachate on an aquatic environment

The treatability of a landfill leachate with respect to the removal of environmentally toxic components was assessed by acute and sub-lethal toxicity testing procedures. A specific leachate that had a 255mgly1 COD and 133mgly1 BOD was used for the research. Acute bioassays (LC50) were undertaken using un-acclimatised juvenile G. pulex (pollution sensitive) and A. aquaticus (pollution tollerant) macro-invertebrates to establish pollution boundaries. The LC50 for A. aquaticus was 60% vyv leachate in clean water, whilst for G. pulex it was only 5%. Remediation techniques (air stripping, aerobic digestion and small-scale reed bed trials) were able to remove the toxicity of leachate towards A. aquaticus but G. pulex obtained a maximum LC50 of 90% vyv treated leachate in clean water. Sub-lethal toxicity tests were carried out at concentrations that were lower than the acute toxicity thresholds for each species. The toxicity was judged on the basis of offspring produced and the growth rate of newly born individuals. As with the acute testing, it was found that A. aquaticus was relatively tolerant to the leachate compared to G. pulex. tests showed that a leachate dilution as high as 1:66 would affect the fecundity of the population of Gammarus, and even a dilution of 1:20 would influence the breeding colony size of Asellus. In contrast, sub-lethal investigations, which used treated leachate as a test media did not influence the fecundity or population size of either test species